feat: Implement server and client metrics collection and monitoring

- Added a new PHP script for collecting server metrics every 30 seconds.
- Created a ServerMonitoring class to handle metrics collection for CPU, RAM, Disk, and Network.
- Introduced database tables for storing server and client metrics.
- Updated server view template to display real-time metrics using Chart.js.
- Added translations for monitoring UI elements.
- Created a new monitoring template for detailed server metrics visualization.
- Implemented client speed tracking and display in the monitoring UI.

bin/collect_metrics.php

@@ -0,0 +1,85 @@
+#!/usr/bin/env php
+<?php
+
+/**
+ * Metrics Collector
+ * 
+ * Runs continuously and collects metrics every 30 seconds
+ * Usage: php bin/collect_metrics.php
+ */
+
+require_once __DIR__ . '/../vendor/autoload.php';
+require_once __DIR__ . '/../inc/Config.php';
+require_once __DIR__ . '/../inc/DB.php';
+require_once __DIR__ . '/../inc/VpnServer.php';
+require_once __DIR__ . '/../inc/VpnClient.php';
+require_once __DIR__ . '/../inc/ServerMonitoring.php';
+
+// Set timezone
+date_default_timezone_set('UTC');
+
+// Enable error logging
+error_reporting(E_ALL);
+ini_set('display_errors', 1);
+
+echo "[" . date('Y-m-d H:i:s') . "] Metrics collector started\n";
+
+// Main loop
+while (true) {
+    try {
+        $startTime = microtime(true);
+        
+        // Get all active servers
+        $servers = VpnServer::listAll();
+        
+        foreach ($servers as $server) {
+            if ($server['status'] !== 'active') {
+                continue;
+            }
+            
+            try {
+                echo "[" . date('Y-m-d H:i:s') . "] Collecting metrics for server #{$server['id']} ({$server['name']})\n";
+                
+                $monitoring = new ServerMonitoring($server['id']);
+                
+                // Collect server metrics
+                $serverMetrics = $monitoring->collectMetrics();
+                echo "  Server: CPU={$serverMetrics['cpu_percent']}% RAM={$serverMetrics['ram_used_mb']}/{$serverMetrics['ram_total_mb']}MB ";
+                echo "Disk={$serverMetrics['disk_used_gb']}/{$serverMetrics['disk_total_gb']}GB ";
+                echo "Net RX={$serverMetrics['network_rx_mbps']}Mbps TX={$serverMetrics['network_tx_mbps']}Mbps\n";
+                
+                // Collect client metrics
+                $clientMetrics = $monitoring->collectClientMetrics();
+                
+                if (!empty($clientMetrics)) {
+                    foreach ($clientMetrics as $cm) {
+                        echo "  Client #{$cm['client_id']} ({$cm['client_name']}): UP={$cm['speed_up_kbps']}Kbps DOWN={$cm['speed_down_kbps']}Kbps\n";
+                    }
+                } else {
+                    echo "  No active clients\n";
+                }
+                
+            } catch (Exception $e) {
+                echo "  ERROR: " . $e->getMessage() . "\n";
+            }
+        }
+        
+        // Clean old metrics
+        ServerMonitoring::cleanOldMetrics();
+        
+        // Calculate sleep time
+        $executionTime = microtime(true) - $startTime;
+        $sleepTime = max(0, 30 - $executionTime);
+        
+        echo "[" . date('Y-m-d H:i:s') . "] Collection completed in " . round($executionTime, 2) . "s, sleeping for " . round($sleepTime, 2) . "s\n\n";
+        
+        if ($sleepTime > 0) {
+            sleep((int)$sleepTime);
+        }
+        
+    } catch (Exception $e) {
+        echo "[" . date('Y-m-d H:i:s') . "] FATAL ERROR: " . $e->getMessage() . "\n";
+        echo "Retrying in 30 seconds...\n\n";
+        sleep(30);
+    }
+}